1. Field of the Invention
The invention relates to a transmission system including a transmitter and at least one receiver, the transmitter including means for transmitting operational signals for a predetermined operation mode of said receiver, and the receiver including means for processing said operational signals in said operation mode.
2. Description of the Related Art
Transmission systems as referred to in the opening paragraph are generally known, inter alia, in the form of conventional radio or television transmission systems. In such systems, the operational signals are conventional radio or television signals. Also known are transmission systems in which operational signals are transmitted in addition to conventional signals so as to offer additional services or to enhance the operation of the receiver. For example, television transmitters transmit stereo sound signals, teletext pages, or electronic program guide information in addition to the normal television program. Television transmitters may also offer an opportunity for the public to actively participate in a television program. Radio transmitters transmit network information, traffic announcements, etc., in addition to the normal radio program.
It is not always clear to a user whether his receiver is equipped to process the operational signals. For example, conventional television receivers do not decode the operational signals which are transmitted along with an interactive television program and which define actions to be carried out by the receiver when a user actively participates, inter alia, by responding to questions in a quiz show or voting for the best performance in a song contest. If such an interactive program is announced to be broadcast, the owner of a modern but conventional receiver is confused about whether or not he can participate. Often, this results in nuisance calls to the service operator, receiver manufacturer or retailer. The confusion will further deteriorate in the near future when further new services will be introduced.
A typical aspect of this type of service is that the relevant operation mode is to be activated by the user. Needless to say that the user will be very frustrated if the service is announced to be available but his attempts to activate the relevant operation mode fail because the operational signals cannot be processed by his receiver.
It is an object of the invention to provide a transmission system by which the above-mentioned problems are alleviated.
To that end, the system is characterized in that the transmitter comprises means for transmitting a logo to indicate the transmission of the operational signals. The receiver comprises means for receiving the logo, comparing the received logo with a locally stored logo, enabling the predetermined operation mode only if the received and locally stored logos are perceptibly identical, and reproducing the logo if said operation mode is enabled.
A logo is herein understood to mean a picture and/or audio tune perceptible by a human. It is preferably designed such that it will be recognized by the public as being associated with a particular type of service.
The invention will be appreciated if it is considered that distinctive logos or audio tunes are easily recognized by the public. It is already common practice to print such logos on apparatuses to identify that they have certain capabilities. The invention extends this idea to the signal domain. By transmitting a logo, it becomes immediately clear to the public that the associated service is being broadcast. By means of the invention, it is achieved that receivers become operating only upon reception of the logo or tune for which they have been designed. New services require transmission of a different logo. Incompatible receivers will not respond to such services. The user will immediately understand that because the logo of xe2x80x9chisxe2x80x9d receiver is not being displayed (either the received, i.e., a different, logo will be displayed or no logo will be displayed at all). Accordingly, the public will not be bothered or confused.
An additional advantage of the invention is the ability to easily trace broadcasters that offer services which are subject to payment of royalty fees, viz., by simply inspecting the logo. This advantage is further enhanced if the logo meets the requirements of being protectable by copyright and/or trademark law.
In an embodiment of the invention, the logo indicates the transmission format of the operational signals. The term transmission format is not restricted to the physical structure (such as modulation type or length of data bits) of the operational signals but also includes the application structure (such as the syntax of data items). It is envisaged that different standards for new services, such as interactive television, will coexist in the future. The logo not only indicates that an interactive program is broadcast, it also identifies the transmission format. With this embodiment, confusion is avoided as to whether or not a receiver is able to decode a transmitted service.
The logo may be separately encoded and transmitted in addition to conventional video or audio signals, e.g., in the vertical blanking interval of an analog television signal or as service information data packets in a digital television signal. The indicator may also be part of the conventional video or audio signal. In that case, the receiver comprises means for extracting the logo from said conventional video or audio signal.
In order to achieve that receivers indeed decode the transmitted logo and remain inoperative if the xe2x80x98wrongxe2x80x99 logo is received, the operational signals may be transmitted in scrambled form, using the logo as a scrambling key. The receiver is adapted to descramble the operational signals using the transmitted logo.